During the game of golf, the golfer strikes the ball to move it instrument termed a golf club, which is constituted by a shaft, and which incorporates a head at its lower end, and, at its upper end, is equipped with a handle or grip.
To drive the ball into the hole, the golfer uses several types of clubs distinguished by the shapes of their heads used to strike the ball and by the length of their shafts. The impact of the ball on the hitting surface of the club head generates, on the shaft, vibratory phenomena which prove especially unpleasant for the golfer, who, after the impact of the ball, feels discomfort which causes him to lose confidence in his club for the next hit.
An analysis of vibratory phenomena has shown that vibrations in a golf club represent the sum of several elementary vibratory phenomena, or modes, whose frequencies range between 0 and 200 Hertz; i.e., a first, vibratory mode in the plane of the swing, of the "free embedded flection" type for which the frequency is approximately 5 Hertz; a second mode of vibration, of the "supported-embedded flection" type, having a frequency of approximately 50 Hertz; a third, torsional mode of vibration whose frequency is approximately 75 Hertz; and a fourth mode of vibration of the first, harmonic flection type, having a frequency of approximately 130 Hertz. The frequency values depend on the properties of the shaft and head, and on the nature of the boundary conditions (site and gripping intensity). All of these vibrations are felt by the golfer as a disagreeable sensation upon impact, and they thus lessen the confidence the golfer has in the equipment, since he anticipates these unpleasant sensations before hitting the ball. It must be noted that the vibration amplitudes are particularly strong because the speed of the club head at the moment of impact is high and because the strokes are off-center.
Different means for reducing vibration amplitudes are known in the art. Complete elimination or attenuation of bad vibrations deprives the golfer of information feedback. In fact, some manufacturers have incorporated, along the entire length of the shaft and in the structure, fibers, e.g., made of Kelvar, which in the context of use, exhibit well-known damping properties so as to reduce energy and thus the amplitudes of the vibrations; however, damping is not selective and, accordingly, the club damps all modes.